1. Field
The present description relates to the field of communications using multiple loop DSL connection and, in particular, to sharing such connections among multiple users.
2. Related Art
Digital subscriber line (DSL) technologies provide potentially large bandwidth for digital communication over existing telephone subscriber lines (referred to as loops and/or the copper plant). Telephone subscriber lines can provide this bandwidth despite their original design for only voice-band analog communication. In particular, asymmetric DSL (ADSL) and very-high-speed DSL (VDSL) can adapt to the characteristics of the subscriber line by using a discrete multitone (DMT) line code that assigns a number of bits to each tone (or sub-carrier), which can be adjusted to channel conditions determined during initialization and subsequent on-line adaptation known as “bit-swapping” and “gain swapping” of the modems (typically transceivers that function as both transmitters and receivers) at each end of the subscriber line.
Currently, VDSL2 systems can achieve data rates of up to approximately 150 Mbps (Megabits per second) on short loops and ADSL2+ systems can achieve data rates of up to approximately 25 Mbps on somewhat longer loops than VDSL. “Short loops” are typically considered to be loops in which the component wires are about 100 meters or less, and in any event no more than 300 meters. Higher data rates are usually limited by the line attenuation on longer loops. On short loops higher data rates are generally limited by the maximum bandwidth used by the ADSL and VDSL modems and by frequency-selective noises caused by crosstalk from other phone lines sharing the same cable, radio ingress, and a variety of customer-premises noises often known generically as impulse noise. These short loops are found at various points in a typical DSL plant.
G-PONs (gigabit passive optical networks) and E-PONs (ethernet passive optical networks) are now used for communications and use optical signals transmitted through optical fiber. Such systems can achieve speeds of ˜1-2.5 Gbps (Gigabit per second) in each direction, using time division multiplexing and upstream dynamic bandwidth allocation. Such a system can have up to 128 customers sharing a line from an optical line terminal (OLT), with each customer having a peak speed of 100 Mbps to 1 Gbps, and average continuous speeds (for example, for use in connection with video) of 20-30 Mbps with 32-128 users. Splitters are placed along such a line for customer drops.
These higher data rate optical systems allow data to be sent at still higher rates to DSL customers. Higher rate DSL service can be provided by using more loops to carry a single stream of packets. However several loops are needed in order to meet the data rates of the optical systems. This many loops are often not available to any one customer. U.S. Patent Application Publication No. 2003/0208772 A1 published Nov. 6, 2003 of Milbrandt describes communicating data for multiple users in which each user receives the same multiple user data on its own single DSL line, but the effect is to reduce data rates.